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W. C. Etheridge 
between 1.5 and 3.5 millimeters. Broili (1910) has described the 
following types: 
1. Short and outstanding. 
2. Long and outstanding. 
3. Long and partly inclosed by the lemma. 
4. Round for its entire length. 
5. Flattened for its entire length. 
6. Flattened, and on the upper third laterally furrowed. 
7. Flattened and furrowed at the base. 
8. Round and hairy. 
DenaifTe and Sirodot (1901) characterize the most general forms of the 
rhachilla, which may used in classification, as follows: 
1. 2.5-3 mm. long, round, and toward the apex gradually swelling into a knob-like head. 
2. 1.5-2 mm. long, more or less flattened and furrowed, and not swollen at the apex. 
Bohmer (1908-09) found, during four years of investigation, that the 
form and length of the rhachilla remained constant. 
In the present study the descriptions of the rhachilla by Broili and by 
Denaiffe and Sirodot have been found accurate but often extremely diffi- 
cult to determine; and, moreover, some of the types are not strictly 
confined to different varieties, but are often combined in the same variety 
or even in the same panicle. Of the characters of the rhachilla here men- 
tioned, none have been considered worthy of use except hairiness, length, 
and, in some varieties, the partial envelopment of the rhachilla by the 
lemma. 
NERVES OF THE GLUME AND THE LEMMA 
In the species of Avena the venation of the glume and of the lemma 
appears as slender, rib-like striations. Such veins are called nerves, 
and when in wild forms those of the lemma extend beyond its apex as 
teeth or awn-points they distinguish the species. Thus, A. brevis and 
A. strigosa are characterized by such awn- or tooth-like projections (Plates 
III, 2, a, and IV, a), while for other species, such as A. pubescens and 
A. Smithii, the number or the scabrous character of the nerves is a dis- 
tinguishing feature. In common cultivated varieties, the lemma is never 
toothed or awn-pointed, and rarely scabrous, but the number and the 
prominence of the nerves are variable, and may in some cases be used in 
classification. DenaifTe and Sirodot (1901), alone of the earlier investi- 
gators, frequently mention the prominence of the nerves of the lemma 
as a minor distinction for varieties within small groups. 
